CVE-2024-21908 in TinyMCE
Summary
by MITRE • 01/03/2024
TinyMCE versions before 5.9.0 are affected by a stored cross-site scripting vulnerability. An unauthenticated and remote attacker could insert crafted HTML into the editor resulting in arbitrary JavaScript execution in another user's browser.
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Analysis
by VulDB Data Team • 11/28/2025
The vulnerability identified as CVE-2024-21908 represents a critical stored cross-site scripting flaw within TinyMCE editor versions prior to 5.9.0. This vulnerability resides in the rich text editor's handling of user input and content processing mechanisms, creating a persistent security risk that can be exploited by unauthenticated attackers. The flaw allows malicious actors to inject crafted HTML content that gets stored within the editor's data structures, subsequently executing arbitrary JavaScript code when other users view the affected content. The vulnerability's classification aligns with CWE-79 which specifically addresses cross-site scripting vulnerabilities in web applications. This particular weakness enables attackers to bypass normal security controls and execute malicious scripts in the context of the victim's browser, potentially leading to session hijacking, data theft, or further exploitation of the compromised user's privileges.
The technical implementation of this vulnerability stems from insufficient input sanitization and output encoding within the TinyMCE editor's content processing pipeline. When users interact with the editor to create or modify content, the system fails to properly validate and escape special characters and HTML tags that could be used to inject malicious scripts. The stored nature of this vulnerability means that once malicious content is successfully injected, it persists in the system and can be executed whenever other users access the affected pages. This makes the vulnerability particularly dangerous as it can affect multiple users over extended periods without requiring repeated exploitation attempts. The remote and unauthenticated nature of the attack vector eliminates the need for attackers to have legitimate credentials or direct access to the system, making this vulnerability accessible to any attacker with knowledge of the target application's usage patterns.
The operational impact of CVE-2024-21908 extends beyond simple script execution, as it creates a persistent backdoor for attackers to compromise user sessions and access sensitive data. When exploited, the vulnerability can enable attackers to steal session cookies, access user accounts, perform unauthorized actions on behalf of victims, and potentially escalate privileges within the affected application. The stored nature of the XSS payload means that even if the initial injection occurs during a brief window, the attack can continue to affect users for as long as the malicious content remains stored in the system. This vulnerability directly violates the principle of least privilege and can be leveraged to perform actions such as modifying content, creating new user accounts, or accessing administrative functions depending on the target application's permissions structure. The attack can be particularly devastating in environments where TinyMCE is used for content management, user-generated content platforms, or collaborative editing systems where multiple users interact with shared content.
Organizations should prioritize immediate remediation by upgrading to TinyMCE version 5.9.0 or later, which includes proper input validation and sanitization mechanisms to prevent malicious HTML injection. Additionally, implementing Content Security Policy headers can provide an additional layer of defense by restricting the sources from which scripts can be executed, thereby mitigating the impact of successful XSS attacks. Security teams should also conduct thorough audits of all web applications utilizing TinyMCE to identify any potential instances of stored XSS vulnerabilities and implement proper input sanitization at multiple layers of the application architecture. The mitigation strategy should include regular security assessments, automated vulnerability scanning, and comprehensive user education regarding the risks of clicking on suspicious links or content within web applications. Organizations should also consider implementing web application firewalls and runtime application self-protection technologies to detect and prevent exploitation attempts, aligning with ATT&CK technique T1059.001 for command and scripting interpreter and T1566.001 for credential harvesting through social engineering. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date software components and implementing defense-in-depth strategies to protect against persistent threats in modern web applications.